This invention relates to conductive adhesive medical electrode assemblies adapted for application adhesively to the skin to provide electrical contact therewith.
This application is related to concurrently filed application Ser. No. 879,876, filed June 30, 1986, whose disclosure is incorporated herein by reference, which claims a sheet of the hydrophilic gel in conductive form employed as a conductive member interfacing with the skin of a patient in the medical electrode assemblies of this invention to provide electrical contact therewith.
Medical electrodes comprising, as a conductive member interfacing with the skin of a patient, a sheet or film of a hydrophilic gel are well known in the art. Hydrogel sheets adapted for use in medical electrode-related applications are commercially produced by Promeon, a Division of Medtronic, Inc. (Brooklyn Center, Minn.); Valleylabs, Inc., a Division of Pfizer (Boulder, Colo.) Biostim, Inc. (Princeton, N.J.); Lectec Corp. (Eden Prairie, Minn.); and Conmed (Utica, N.M.).
Numerous U.S. patents disclose hydrophilic gels and medical electrodes employing them. The following illustrate the early state of that prior art.
U.S. Pat. No. 3,357,930 (electrically conductive transparent films comprising a polymeric matrix in gel form, a plasticizer therefor, an ionized electrolyte soluble in the plasticizer, and an ionizable solvent, e.g., solid polyvinyl alcohol, glycerine, lithium chloride and silica).
U.S. Pat. No. 3,911,906 (electrode with skin interfacing film of a pressure sensitive adhesive containing fine electrically conductive particles, e.g., an acrylic copolymer containing carbon powder).
U.S. Pat. No. 3,993,049 (electrode comprising a pliant patch of a formaminated material covered on the side adapted to be placed on the skin with a salt-containing adhesive).
U.S. Pat. No. 3,994,302 (stimulating electrode in which the skin contacting element is an ion-exchange material, e.g., a vinyl pyridine grafted to a polyethylene base).
U.S. Pat. No. 3,998,215 claims an electrically conductive pad which employs a hydrogel impregnated with a fibrous carrier. The polymers disclosed herein as operable require a chemical cross-linking agent. The commercial version thereof sold by the patentee (Minnesota Mining and Manufacturing Co.) has poor skin adhesion and contains bubbles (the latter presumably due to the viscosity of the starting gel and/or the technique employed to impregnate the fibrous carrier with the starting polymer solution). Bubbles in the conductive pad are undesirable because they create local areas of altered electrical properties.
Since the issuance of U.S. Pat. No. 3,998,215, numerous other patents employing a hydrophilic gel as an electrically conducting means which interfaces with the skin of the patient have issued. The following are illustrative of such patents.
U.S. Pat. No. 4,008,721 (tape electrode comprising a skin-contacting layer of adhesive material, e.g., acrylic copolymer).
U.S. Pat. No. 4,054,714 (electrically conductive adhesive useful for binding together surfaces of electronic devices, comprising a polymeric binder, conductive particles whose surfaces are a noble metal and a normally liquid polyhydric alcohol).
U.S. Pat. No. 4,067,342 (tape electrode for transmission of electrical signals into the body through the skin employing a tape having a surface of a conductive material combined with an adhesive e.g., acrylic polymer adhesive, and a second surface with the conductive material comprising a magnetic substance.)
U.S. Pat. No. 4,094,822 (electrode having a cup, which is taped to the skin, containing a semi-solid adhesive polymeric material, e.g., a mixture of polyvinyl alcohol, boric acid, CMC, glycerol and water and an electrolyte, e.g., AgCl or a zinc salt).
U.S. Pat. No. 4,066,078 (electrode with a skin interfacing film having adhesive, plastic and hydrophilic properties, e.g., produced from an interpolymer comprising (a) 10-90 parts of an ester of an .alpha.,.beta.-olefinically unsaturated carboxylic acid and a mono- or polyhydric alcohol; (b) 90-10 parts of an .alpha.,.beta.-olefinically unsaturated comonomer; and (c) at least 0.02 parts of a cross-linking agent comprising a difunctional monomer.)
U.S. Pat. No. 4,092,985 (disposable electrode comprising an elastically stretchable layer of water permeable porous webbing permeated with a high water content liquid or semisolid conductive medium).
U.S. Pat. No. 4,109,648 (electrode assembly comprising a self-supporting body of hydrogel, e.g., hydroxyethyl methacrylate polymerized with ammonium persulfate and sodium metabisulphite around graphite fiber).
U.S. Pat. No. 4,125,110; U.S. Pat. No. Re. 31,454 (electrode comprising as a skin interfacing substrate, a colloidal dispersion of a naturally occuring hydrophilic polysaccharide such as karaya, and a salt in an alcohol as a continuous phase).
U.S. Pat. No. 4,141,366 (electrode for transmitting electrical signals through the skin employing a normally "dry" adhesive which is activated at the time of application by a suitable solvent).
U.S. Pat. No. 4,273,135 (an essentially dry electrode employing as the conductive interface a cohesive, conformable, nonionic hydrophilic synthetic polymer plasticized with a monomer, e.g., glycerol. The electrode is applied to abraded skin wet with normal saline solution or water). This patent contains a detailed description of prior art electrodes in addition to those described and claimed (herein).
U.S. Pat. No. 4,274,420 (an electrode similar to U.S. Pat. No. 4,125,110 in which the adhesive substrate comprises a karaya gum matrix supporting an electrically conductive fluid).
U.S. Pat. No. 4,300,575 (an electrode with a conductive element composed of karaya, carbon black, isopropyl alcohol and karaya gum conductive solution).
U.S. Pat. Nos. 4,317,278; 4,318,746 and 4,362,165 electrodes comprising an annulus of foam with an electrode gel in the central region of the annulus, which gel is the subject of U.S. Pat. No. 4,318,746 and is composed of two polymers, one of which is hot water soluble, e.g., kappa carrageenan, and the other is not, e.g., hydroxypropylmethylcellulose, and which contains a potassium salt to enhance the gel's conductivity.
U.S. Pat. Nos. 4,365,634; 4,393,584; and 4,522,211 (electrodes with adhesive layer secured to a semi-flexible plastic-like sheet, and formed from a known electrically conductive adhesive, e.g., Johnson & Johnson Co.'s "Bioadhesive", disclosed in U.S. Pat. No. 4,066,078, or in U.S. Pat. Nos. 4,008,721; 3,998,215; 3,993,049; and 3,911,906; preferably a hydrophilic material disclosed in U.S. Pat. Nos. 3,822,238, 4,156,066 and 4,156,067).
U.S. Pat. No. 4,383,529 (iontophoretic electrode device with a semi-solid hydrophilic hydrated gel formed, e.g., from agar, a protein or a synthetic polymer, e.g., methyl cellulose).
U.S. Pat. No. 4,458,696 (TENS electrode with an extensible interfacing layer of up to 10 mils thickeners comprised of a carrier portion coated with an electrically conductive adhesive, preferably a 75:25 butyl acrylate-acrylic acid copolymer neutralized with methyl diethanolamine to which are added a water-soluble plasticizer and tackifier, as described in U.S. Pat. No. 3,065,770).
U.S. Pat. No. 4,515,162 (electrode pad comprising a tacky crosslinked hydrogel adhered to an electrode terminal plate, e.g., a polyacrylic acid and a polyacrylic acid salt, water, and a compound containing at least two epoxy groups, as cross-linking component, and optionally a tackifier, e.g., glycerine, propylene glycol or polyethylene glycol, an electrolyte material, e.g., sodium chloride or potassium chloride, a pH controlling agent, a flexibility imparting agent, an antifungal agent, and the like).
U.S. Pat. No. 4,524,087 (electrode with a conductive adhesive thereon which is swellable, dermally-nonirritating conformable, coadhesive, ionic hydrophilic polymer, e.g., produced by UV polymerizing a mixture consisting of triethyleneglycol-bis-methacrylate dissolved in acrylate acid to which is added glycerol and potassium hydroxide in water, using a free radical initiator to initiate polymerization, e.g., a photoinitiator).
U.S. Pat. No. 4,543,958 (electrodes with conductive adhesive film comprising a naturally occurring karaya gum, e.g., available in sheet form from Lectec Corp. or as described in U.S. Pat. Nos. 3,357,930; 3,993,049; 4,066,078; and 4,141,366).
The preferred hydrophilic gels of this invention fall within the broad class of cross-linked polyethylene oxide polymers described in U.S. Pat. Nos. 3,264,202 and 3,419,006. See also U.S. Pat. Nos. 3,898,143; 3,993,551; 3,993,552; 3,993,553 and 3,900,378.
Although there exists in the prior art numerous teachings of medical electrodes having a hydrophilic gel as a skin interfacing member, none meet all the criteria of an optimum medical electrode, i.e., a dermatologically inert skin interfacing member, i.e., one which contains no organic solvents, residual monomer chemical cross-linking agents or substantial quantities of uncrosslinked adhesive polymer; it is a viscoelastic solid, i.e., it readily conforms to non-flat areas of the skin; it is sufficiently adhesive to adhere firmly to the skin, so that there is little likelihood of it falling off during use, yet it is not so adhesive that it causes pain and/or damage to the skin upon removal; it is adequately adhesive to moist as well as to dry skin and to soiled as well as to clean skin, so that skin pre-preparation with organic solvent or abrasive is not required; it has superior electrical properties, such as low impedance and low offsets; it has a good shelf life in its unopened package; and its properties do not readily deteriorate between the time the package in which the electrode is sealed is opened and before or during use. The medical electrodes of this invention possess all of these and other advantageous properties for long term use.